Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$97.42	5.433%	$102.7128	$102.71	$102.70	$102.70
Purchase #2	$165.58	3.514%	$171.3985	$171.40	$171.40	$171.40
Purchase #3	$28.70	9.633%	$31.4647	$31.46	$31.45	$31.50
Purchase #4	$97.87	5.314%	$103.0708	$103.07	$103.05	$103.10
Purchase #5	$200.31	10.586%	$221.5148	$221.51	$221.50	$221.50
Purchase #6	$120.86	9.704%	$132.5883	$132.59	$132.60	$132.60
Purchase #7	$90.28	13.265%	$102.2556	$102.26	$102.25	$102.30
7 purchase totals =	$801.02		$865.0055	$865.00	$864.95	$865.10